The present invention relates to sewage disposal systems and, in particular, to an improved drain field construction for economically maximizing the exposed percolation surface area while permitting evaporation through covered mesh-like channel defining members and from which members lengths of drain tile are suspended.
Home sewage systems have long formed a part of rural living with each home or waste generating facility having an associated septic tank for containing liquid and solid waste matter and from which the waste is either periodically pumped into tank trucks or returned to the soil as grey water via the drain field. It is with respect to the latter type of disposal system that the present invention is directed and wherein the septic tank is typically coupled to a downstream distribution box and from which a plurality of trenches and drain lines radiate and serve to distribute and return the grey water and decomposed solid matter to the soil, whereat it is absorbed and filtered by the soil before entering the ground water.
Initially, during the sizing of a drain field, the amount of required soil surface area is determined in relation to the projected amount of effluent that the field will serve and the percolation rate of the soil itself. Upon performing percolation tests on the soil to determine the rate at which the effluent will be absorbed, a desired percolation area and corresponding length and number of trenches can be determined for a given size dwelling.
While the actual construction for any given sewage system will depend upon pertinent plumbing codes, a drain field is typically constructed to include a plurality of trenches dug to a width of approximately three feet and to a depth of not exceeding three and a half feet. Thus, for one hundred lineal feet of trench, approximately three hundred square feet of surface percolation area is provided for absorption. Each trench being typically back filled with gravel of an average aggregate size of approximately one inch and over which the drain tile is placed before the trenches are further back filled with rock and finally the removed top soil.
In terms of manpower and equipment, the above construction requires equipment for trenching the individual lines, equipment for conveying to and filling the trenches with the gravel or rock and equipment for backfilling the drain field, once completed. As labor and equipment costs have risen, not to mention the rising cost for the gravel itself, it has therefore become a more costly matter to install such systems. Consequently, the present invention was conceived in order to reduce these costs, while providing an equally efficient system and possible a system that may be used with previously marginal soils. In particular, the present invention achieves these and other ends via a modularly constructed apparatus which mounts within the individual trenches in a fashion so as to replace the gravel previously used, while forming hollow porous mesh-like channels within which the effluent may be received, before being absorbed by the soil and/or evaporating through the walls of the channel to the surface and air.
Two previous attempts at developing drain fields not requiring rock filler media can be seen upon directing attention to U.S. Pat. Nos. 3,579,995 and 4,415,157. Of these attempts, the former discloses a vented leeching channel that is assembled from a plurality of lengthwise connected cast concrete structures. Each so-called "shed-like structure" contains a plurality of apertures through its sidewalls and a plurality of aperture protecting lips for preventing against the filling of the channels with dirt. The latter patent discloses a molded plastic drain field section having a center-mounted drain pipe and associated side troughs, which together permit the replacement of the rock filler. In use, however, the actual amount of soil exposed to effluent is limited by the soil exposed to the side troughs. For both of these patents, too, evaporative action is limited by the solid upper construction of the channel forming members and upon which the back filled dirt rests.
Various other unrelated irrigation/drainage assemblies have also been noted in U.S. Pat. Nos. 463,871; 988,639; 1,608,889; 3,333,422; 3,440,823; 4,102,135; and 4,188,154. Each of these, however, is intended for the distribution or removal of liquids in other than drain field applications and then without concern for decomposing materials contained within the liquids.
Because of the above-mentioned cost concerns and need for an absorptive/evaporative drain field, the present invention was conceived and which comprises a modularly constructed drain field having a plurality of lengthwise connected, air permeable channel forming meshwork members that are capable of supporting the overlying top soil. Suspended from the channel forming members are a plurality of lengthwise connected drain pipes or conduits for appropriately conveying to the effluent within the drain field. When assembled, drain fields of the present type provide the following advantages: (1) they provide a greater absorption surface area per lineal foot of trench, thus permitting a reduction in the overall drain field size; (2) they permit pumping and periodic maintenance in order to extend the life of the drain field; (3) they permit evaporation; (4) they provide an increased volume capacity within the channel; and (5) they require less equipment and labor to install than previously required.
The above objects, advantages and distinctions as well as the construction of the present invention will, however, become more apparent upon directing attention to the following description thereof with respect to the appended drawings. Before referring thereto, though, it is to be recognized that the present description is made with respect to the presently preferred embodiment only and that, accordingly, various modifications may be made thereto, such as in the shape or configuration of the channel, type of materials used, etc. without departing from the spirit and scope thereof.